It is desirable to provide a multi-layer golf ball having a cover comprised of multiple layers to allow manipulation of material properties to provide desired characteristics such as spin rate, initial velocity, feel to the user, and durability. This has been done in the past by mixing different resins to create a single layer cover with the proper characteristics, or by creating multi-layer balls from successive layers of different resins, each layer providing different beneficial characteristics.
A typical multi-layer balls application is described in U.S. Pat. No. 4,431,193, issued Feb. 14, 1984 to Nesbitt. Two different layers of SURLYN (a trademark of E.I. du Pont De Nemours Co. for ionomer resins) materials are successively molded about a golf ball core to form a multi-layer ball. The outer layer is chosen primarily for the feel it provides to the user, and the inner layer is chosen primarily for its structural properties. One prior art method of molding the cover layer of a golf ball around the core of the golf ball is to support the golf ball core within an injection mold using retractable pins extending from the inner surface of the mold to the surface of the core. These pins touch and support the core in the center of the mold while the cover material is injected into the mold. Once the mold is substantially filled with the cover material, the pins are withdrawn and the cover material fills the cavity between the core and the mold. The cover material is then allowed to solidify in the mold.
Alternatively, two molded hemispheres can be placed around the core of the golf ball and be compression molded to produce a cover layer. The compression molding process involves forming the cover around the core under heat and pressure.